1. Field of the Invention
This invention relates generally to air circulation systems for vehicle heating and cooling systems, especially for heating and cooling the passenger compartment and other pertinent compartments of motor vehicles. The invention more particularly concerns apparati and methods for improving the air quality in such systems. More specifically, the invention comprises apparatus and methods for causing the air flow to pass through a decontamination module to clean the air. Additionally, the invention controls the extent of such cleaning by a by-pass and damper arrangement, which apportions the flow between the module and the by-pass. The invention has application to both new vehicles as original equipment and older vehicles as added equipment.
2. Related Art
Air conditioning systems within moving vehicles generally serve two important functions. One function is to provide means for comfortable in-vehicle conditions for all vehicle occupants. Another function is to guarantee good visibility through all windows. In fact, many countries require by law that the heating function be capable of keeping the windows free of mist and ice. (e.g., within the European Community by Guideline EWG 78/317 and in the USA by Safety Standard MVSS 103).
Motor vehicles generally employ either a liquid cooled S1 or C1 engine or an air-cooled S1 or C1 engine.
Typically, in vehicles with liquid-cooled S1 or C1 engines, the interior is heated by the waste heat from the engine. In vehicles with air-cooled S1 or C1 engines, heat given off by the engine oil may also provide heat to the interior.
Typical vehicle heating and cooling systems comprise two major components. One component, the "air condition component," functions to heat, cool and supply air to the passenger compartment. Consequently, it includes a blower which circulates the air, a heater core for heating the air, and the evaporator core of a refrigeration unit for cooling the air. The second component, the "air distribution component," operates to distribute the air to various outlets within the passenger compartment. The distribution of the air may be controlled either manually or automatically. In either case, a series of doors or dampers is manipulated to direct the flow through the appropriate core. Additionally, a series of selection devices and switches activates the heater core or the air cooling evaporator core as desired. Further, an air inlet door leading to the blower is adjustable to supply air to the system solely from the atmosphere, to recirculate the air from the passenger compartment, or to provide a mixture of outside and recirculated air.
The air distribution component necessarily comprises ductwork and outlets within the passenger compartment. In general, the outlets may include floor outlets, outlets in or below the dashboard, and defroster outlets for the front windshield. Typically, warm air is delivered by the floor outlets and the defroster outlets. Cool air, on the other hand, generally flows from the dashboard outlets. As with the air condition component, a series of dampers, selected manually or automatically, routes the air supply to the appropriate outlets. Some outlets contain louvers which enable the passengers to direct the air flow from the outlets as desired.
For most purposes and in most vehicles, the conventional air conditioning systems described above perform quite satisfactorily. However, the condition of the environment both outside and inside the vehicle is an area of growing interest and concern. Of particular concern is the effect of contaminants within the environment on the vehicle's passengers. For example, many persons are allergic to pollens, spores and other products of nature. Additionally, industrial contaminants, such as chemical gases and vapors, also cause allergic reactions in many persons. Most persons, whether allergic or not, object strongly to strange or bad odors. Like the allergens discussed above, offensive odors may be natural or industrial in origin. For example, some people find the odor of upholstery installed in vehicles to be objectionable. Still other persons object to the smell of gasoline vapors and gases such as hydrogen sulfide, sulfur dioxide, and engine exhausts.
Typical air conditioning systems are not designed to deal with air contamination, although steps have recently been taken to address this problem. Modern automobile cabin air filtration systems that reduce the particulates entering the interior have been available in Europe for several years. (See AUTOMOTIVE ENGINEERING 58, May 1995) Recently, manufacturers have begun to adapt these filters to reduce odorous gases and vapors caused by exhaust fumes, industrial processes, farms (animals), and air conditioning systems. Because of the wide variety of odorous materials and sources, and because of the wide range of odor threshold levels for those materials, these filters generally employ activated carbon as the primary odor-reducing medium. The activated carbon operates to remove many of the undesired components through physical or chemical adsorption or catalytic reactions in the activated carbon pore structure. Whatever the choice of particulate adsorbent, the adsorbent is typically present as a bed through which the air is passed.
Other types of filters and threatening agents that have been mentioned include electrostatic filters, chemisorbents, catalytic adsorbents, and chemical neutralizers.
Activated carbon filters generally work well to remove higher-molecular-weight, low-vapor-pressure organic components via physical adsorption. However, for the efficiency of physical adsorption to be maximized, it must occur at relatively low temperatures. Unfortunately, many lower-molecular-weight compounds and highly volatile materials such as hydrogen sulfide, ammonia, and sulfur dioxide are not effectively removed by activated carbon via physical adsorption. To remedy this problem, chemical impregnants can be added to the activated carbon. Such chemical impregnants give the activated carbon chemical adsorption (chemisorption) or reaction properties.
Since chemisorption is essentially a chemical reaction, it is generally more effective at higher temperatures due to improved reaction rates. It is noted, however, that treatment of the activated carbon with impregnants may have an adverse effect on physical adsorption efficiency. As a result, producers of such filters have necessarily had to balance physical and chemical adsorption properties to provide maximum effectiveness for a wide range of compounds. Such concessions necessarily allow a number of undesired particulates and odors to enter the vehicle cabin.
It appears that air conditioning systems which employ the above-described filters channel all of the air circulating in the system through the filter without regard to the amount of contaminants in the air. Such use amounts to a costly and inefficient method of removing undesired particulates and odors in that the filters will necessarily need to be replaced more often and air circulation through the system may be less efficient causing a decrease in gas mileage, etc.
Another problem associated with systems currently in use is their inability to decontaminate recirculated air. Recirculated air is air which is drawn from the vehicle interior, travels through the vehicle's air conditioning system and is redistributed to the vehicle interior. Recirculated air contains no outside air. As such, these systems appear to be capable only of cleaning outside air entering the vehicle through the vehicle's air conditioning system. This causes a problem in providing complete occupant comfort in that offensive interior odors and particles, such as cigarette smoke or outgassing from carpet, etc., cannot be adequately removed.